/Engine/Source/Runtime/Slate/Public/Framework/MultiBox/MultiBox.h
Adds a widget to MultiBoxWidgets map, to access and modify its visibility based on search filters
void AddElement ( [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [SWidget](API\Runtime\SlateCore\Widgets\SWidget) > BlockWidget, [FText](API\Runtime\Core\Internationalization\FText) BlockDisplayText, bool bInSearchable )